Due to energy costs and conservation, there is a demand for refrigerant motor-compressor systems which have an output which can be varied in accordance with demand. To satisfy this demand, a large number of systems have been developed. One such system involves the unloading of one or more cylinders in a multi-cylinder compressor or the varying of re-expansion volume for the purpose of varying the output of the compressor system. These variable capacity systems tend to be relatively complex and the efficiency of the compressor in an unloaded stated is not optimum. Variable speed compressors have also been used, but these variable speed compressors require expensive controls. The efficiency of the speed control, as well as the efficiency of the motor-compressor, present problems at least when the system is operating in a reduced capacity condition.
Compressor systems have also been developed which, in place of a single compressor large enough to carry the maximum load demand, include a plurality of smaller motor compressors having a combined output equal to the required maximum load demand. These multi-compressor systems include means for controlling the total system in such a manner as to selectively activate and deactivate each of the plurality of motor compressors independently when the load demand varies so that the compressor system output meets the required load demand. These multi-compressor systems have good efficiency but they require complex piping and plumbing systems, including means for dealing with lubricating oil management in order to ensure that all of the lubricating oil remains equally distributed between each of the individual compressors.
Additional designs for the multi-compressor systems have included the incorporation of a plurality of standard motor compressor units in a common single compressor shell. The common shell maximizes the compactness of the system and it provides a common oil sump for equal oil distribution, a common suction gas inlet and a common discharge gas outlet. These single shell multi-compressor systems have proved to be acceptable in the market place, but they tend to be relatively large and the means for controlling the total system is still somewhat complex.
The continued development of multi-compressor systems has been directed towards reducing the overall costs and the overall size of the system as well as simplifying the control systems which determine the compressor system's output in relation to the system demand.
The present invention provides the art with a multi-compressor compression system where a single compressor is located at opposing sides of a single drive shaft. A single motor rotor is press fit to the central portion of the drive shaft and the single motor rotor is disposed within a single motor stator. Thus, both compressors are powered by the same rotor and stator of a single motor. The control of the output of the multi-compressor system is accomplished by a variable speed motor or by a pulsed width modulation (PWM) capacity control system incorporated into one or both of the opposing compressors. When incorporating a variable speed motor for capacity control, the capacity can be varied from 0% to 100%. When incorporating the PWM capacity control system into one of the compressors, the capacity can be varied from 50% and 100%. When incorporating the PWM capacity control system into both compressors, the capacity can be varied from 0% to 100%. The capacity of one or both of the compressors can be increased to approximately 120% of capacity using a vapor injection system to further increase the range of the dual compressor system if desired. More than one of these dual-compressor/single motor systems can be incorporated into a single shell if desired.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.